Heat Pump Replacement Cost UK: Repair or Replace?

Heat Pump Replacement Cost UK: When It’s Worth It and When It Isn’t

When a heat pump starts costing too much, running badly or throwing fault codes, replacement is usually the first thought. It’s also the most expensive answer on the table. Before you ask for quotes, it helps to know what replacement really costs, when it’s justified, and how often the heat pump isn’t the problem at all.

The Short Answer

Replacing a heat pump typically costs about the same as a new installation, commonly £8,000 to £15,000 or more before any grant, depending on the unit, the hot water cylinder, the pipework and the electrical work. A repair is usually a fraction of that. And many heat pumps that seem to be failing are running on poor settings or a poorly designed system, which a new unit won’t fix.

What Does a Heat Pump Replacement Cost?

The total is made up of several parts:

• The heat pump itself. The outdoor unit, and sometimes an indoor unit or hydrobox.

• The hot water cylinder, if the old one isn’t compatible or is nearing the end of its life.

• Controls and sensors, which often need updating with the new unit.

• Pipework and radiators. If the original design was wrong, a proper replacement means fixing it, which adds cost.

• Electrical work, such as a new isolator, supply upgrade or consumer unit changes.

• Labour, commissioning and certification.

A like-for-like swap can cost less than a first installation, because the pipework and electrics are already in place. But if the original system was poorly designed, a cheap swap just repeats the same problems with a new badge on the outside. Our guide on how much heat pump installation costs in the UK breaks down the typical figures in more detail.

When Replacement Is Genuinely the Right Call

Replacement makes sense when the unit itself has reached the end of its useful life:

• Age. Many air source heat pumps are commonly quoted as lasting around 15 to 20 years. Our guide on how long an air source heat pump lasts covers what affects that.

• Repeated major failures, such as compressor or refrigerant circuit problems, especially on an older unit.

• Parts that are no longer available, or a manufacturer that no longer supports the model.

• A repair quote that comes close to half the cost of replacement. This is a rule of thumb rather than a rule, but it’s a useful sanity check. Our article on heat pump repair costs in the UK shows what typical repairs cost.

• Poor efficiency on an old unit even after the system around it has been properly tuned.

When It Probably Isn’t the Heat Pump

These symptoms are often blamed on the unit, and they rarely mean it’s dead:

• Electricity bills much higher than expected

• Some rooms never warm up

• The heat pump runs constantly, or switches on and off every few minutes

• Fault codes that clear and come back

• A house that doesn’t hold temperature, even though the heat pump seems to be working

In most of these cases the cause is a flow temperature set too high, weather compensation switched off, too many heating zones, poor balancing or an incorrect sizing. We’ve seen all of them on real homes:

• A new build in Essex with nine underfloor zones was running at a COP of just 1.2. A brand-new heat pump would have shown exactly the same efficiency. Cutting the zones to two and lowering the flow temperature fixed it.

• A family home’s bills doubled when the heat pump was running at 55°C in mild weather. The unit was fine.

• In a 1930s house in Leeds, the homeowner was told the microbore pipework needed replacing, a quote of £8,000 or more. Measurements showed that re-piping two radiators was enough.

The Risk of Replacing the Wrong Thing

A new heat pump connected to the same pipework, radiators, zoning and settings tends to recreate the same problems. If the old unit was oversized or undersized, a replacement chosen the same way will be too. Our guides on what happens if a heat pump is oversized and the signs of an undersized one explain how it happens.

If you do decide to replace, the sizing and design need to be right this time. That starts with a proper heat loss calculation, not a guess based on the old unit.

Repair or Replace? Five Questions to Ask

1. How old is it? Under 10 years, repair is usually more sensible. Over 15, replacement becomes a real option.

2. What does the repair cost compared with replacement? If repair is close to half the cost of a new system, think hard.

3. Is the fault in the unit, or in the system around it? This is the question most people skip, and the most important one.

4. Are parts and support still available? A repair is only worth it if it can be done properly.

5. Is anyone else responsible? If the heat pump is relatively new, the installer or manufacturer may owe you a fix under warranty or their workmanship guarantee.

What About Grants?

The Boiler Upgrade Scheme is designed to help households replace fossil fuel heating with a heat pump. Replacing an existing heat pump is usually not eligible, so don’t plan around a grant unless you’ve confirmed it under the current scheme rules.

How to Check Before You Spend Thousands

The cheapest step is to have the system looked at before you commit. A remote diagnosis can tell you whether the problem is the unit, the settings or the way the system was designed, for a fraction of the cost of a replacement. If it does turn out the unit has to go, you’ll know exactly why, and you’ll have the right information to give to installers.

If you’re already holding a replacement quote, our Pre-Installation Design Review checks the sizing, flow temperature and radiators before you sign. And if you’d like accurate room-by-room figures first, a Heat Loss & Plumbing Survey gives you the numbers.

Frequently Asked Questions

How much does it cost to replace an air source heat pump?
Typically £8,000 to £15,000 or more before any grant, depending on the unit, cylinder, pipework and electrical work. A like-for-like swap on a well-designed system can cost less than a first installation.

Is it worth repairing an old heat pump?
Often yes, if the unit is under about 15 years old and the repair is far cheaper than replacement. If a repair would cost close to half of a new system, or the same major part keeps failing, replacement deserves a serious look.

Can I replace just the outdoor unit?
Sometimes, if the new outdoor unit is compatible with your existing indoor unit, cylinder and controls. Compatibility varies by manufacturer, so check before you buy.

Will a new heat pump lower my bills?
Only if the heat pump itself was the cause. If the high bills come from flow temperature, zoning, sizing or settings, a replacement connected to the same system will usually produce the same bills.

How long do heat pumps last?
Many are commonly quoted at around 15 to 20 years, depending on the make, how well they were installed and how well they’ve been serviced.

Does the Boiler Upgrade Scheme cover replacing a heat pump?
It’s designed for replacing fossil fuel systems, and replacing an existing heat pump is usually not eligible. Check the current scheme rules before you plan around it.